Coded light (CL) has been proposed to enable advanced control of light sources. Coded light is based on embedding of data, inter alia invisible identifiers, in the light output of the light sources. Coded light may thus be defined as the embedding of data and identifiers in the light output of a visible light source, wherein the embedded data and/or identifier preferably do not influence the primary lighting function (i.e. illumination) of the light source. Hence, any modulation of the emitted light pertaining to data and/or identifier should be invisible to humans. This allows for applications such as interactive scene setting, commissioning and re-commissioning of networked lighting systems. Coded light may be used in communications applications wherein one or more light sources in a coded lighting system are configured to emit coded light and thereby communicate information to a receiver. Also the light sources of the coded lighting system may be capable of bidirectional communications utilizing coded light. Thus coded light may be associated with the term visible light communication.
In a CL system, it may be desirable to identify and control the light sources in a given environment or in the proximity of a user or operator. For typical office environments such a coded lighting system may include in the order of 5 to 10 light sources. For future ambient creation systems (inter alia for retail) based on light emitting diodes (LEDs) the number of light sources could be at least one order higher, i.e. 20 to 200 light sources.
For identification and control of each light source, a light source should be distinguishable from all other light sources in the control network, not only local. In office environments, as an example, this control network may cover the whole building and might include 1000 light sources. The CL address space assigned for this environment should then at least include 1000 addresses, hence corresponding to 10 binary digits (bits).
In some system architectures, it might moreover be required to transmit coded light comprising a specific address format which might be even much longer. For example, in a first commissioning phase the light sources might be required to transmit the Internet protocol (IP) or media access control (MAC) addresses of the local lighting controller, inter alia based on the digital addressable light interface (DALI), followed by the assigned control address of the light sources, inter alia the DALI address. This might result in addresses of 70 bit length. Alternatively, a factory embedded unique identifier could be embedded in the light source/driver.
The size of the required address space makes that the preferred CL modulation techniques, such as code division multiple access (CDMA) and frequency division multiple access (FDMA), cannot be applied efficiently. This is caused by the fact that these are typically limited to, due to practical implementation issues, much smaller number of unique codes or frequencies, for CDMA and FDMA, respectively.
WO2007/095740 discloses a light source configured to send a beacon signal representative of the unique identifier thereof, on command, constantly or at a predetermined interval. The beacon signal is integrated into the light emitted by the light source, wherein the integration of the beacon signal is performed in a manner that visible flicker of the resultant light is imperceptible. A remote detection unit is configured to receive the light and extract the beacon signal therefrom. In this manner the remote detection device is capable of wirelessly determining the unique identifier of a light source.
For advanced user interaction with a lighting system one wants to identify, and estimate the strength of, the local light sources. This is enabled by CL. When worldwide or control network wide unique, and consequently long, addresses or codes are applied, however, efficient CL modulation methods cannot be applied to their best extent. This results in a long response time of the system, which might turn out to be unacceptable for some applications. Also, the suboptimal assignment of addresses or codes between the light sources might result in decreased performance in illumination contribution estimation.
Furthermore, the number of addresses needed to identify a light source globally may be two orders larger than what is needed to control the light sources in the local proximity or in a room.